The present invention relates to a pressure meter, and more particularly to a pressure meter of a simple structure and a small size which is capable of digitally displaying a desired preset pressure and a preset pressure of a pressurized fluid through a simple operation.
It is customary to connect a pressure meter to a fluid pipe for checking whether a fluid under pressure, such as air under pressure, is supplied to an actuator and the actuator is operated under a normal pressure. If the fluid pressure supplied to the actuator is abnormally low or high, the actuator or various devices driven by the actuator may be damaged or cause a dangerous situation for a worker or workers working in the vicinity. Therefore, a variety of pressure meters have heretofore been developed and used in fluid supply systems. Many conventional pressure meters employ Bourdon tubes or diaphragms, and are bulky and poor in the accuracy of pressure detection.
One conventional pressure meter A using a Bourdon tube is illustrated in FIGS. 1(a) and 1(b). As shown in FIG. 1(a), a display or indicator 4 with numerals printed for displaying fluid pressures in an analog fashion is mounted in a cylindrical casing 2. A pointer needle 6 is disposed centrally in the display 4 for rotation about the axis of the casing 2. A pin 8 is mounted on the display 4 for preventing the pointer needle 6 from rotating counterclockwise beyond a certain range.
As illustrated in FIG. 1(b), a support 12 defining a passage for supplying a fluid under pressure to a curved Bourdon tube 10 is disposed in the casing 2. A base plate 14 is mounted on the support 12, and a shaft 16 coupled to the pointer needle 6 is mounted on the base plate 14. A spring 18 is connected at one end to the shaft 16, over which a gear 20 is fitted. The gear 20 is held in mesh with teeth 24 on one end of an arm 22, the other end of which is connected to a first curved rod 26. The curved rod 26 engages one end of a straight rod 28, with its other end engaging the distal end of the Bourdon tube 10. An externally threaded fitting 30 defines a fluid passage therein for supplying a fluid pressure to the Bourdon tube 10.
In use, the externally threaded fitting 30 is threaded into a fluid pressure pipe and fixed thereto. As a result, a fluid under pressure is supplied through the fitting 30 into the Bourdon tube 10. When the fluid under pressure is supplied into the Bourdon tube 10, the distal end thereof is flexed to cause the rod 28 and the curved rod 26 to displace the arm 22, whereupon the teeth 24 rotate the gear 20. The pointer needle 6 coaxially connected to the gear 20 is thus rotated clockwise to indicate the numeral corresponding to the fluid pressure in an analog manner on the display 4. The spring 18 urges the shaft 16 to counterbalance its rotation under the fluid pressure supplied into the Bourdon tube 10.
With the above construction, the Bourdon tube 10 must be hermetically joined as by brazing to the support 12. The Bourdon tube 10 itself takes up a considerable area within the casing 2. Various mechanical elements such as the spring 18, the gear 20, the curved arm 22 including the teeth 24, the curved rod 26, the rod 28 engaging the Bourdon tube 10, etc., must be assembled in the casing 2. Fine adjustment must be carried out by a skilled worker to position these elements for increased measurement accuracy.
The display 4 indicates fluid pressures in an analog manner. Such analog numerical representation together with possible reading errors fails to detect pressures with accuracy.
Heretofore, it has been a known practice to couple a pressure switch to the pressure meter so that when the supplied fluid pressure is lower or higher than a prescribed level, the pressure switch operates to stop the supply of the fluid under pressure to the pressure meter. One conventional pressure switch is shown in FIG. 2 of the accompanying drawings. The pressure switch, generally denoted by the reference numeral 32, has a piston 36 with a magnet, the piston 36 being slidably disposed in a casing 34. Displacement of the piston 36 is limited by a spring 40 with its resiliency adjustable by turning an adjustment screw 38 and a fluid under pressure introduced from a passage 42. A switching element 44 is disposed alongside of the piston 36, the switching element 44 being operable by the magnet associated with the piston 36.
Therefore, the amount of movement of the piston 36 which is displaced by the fluid pressure is detected by the switching element 44, which issues an output signal for controlling a machining apparatus, for example, to actuate or stop the same.
Where the pressure switch 32 (FIG. 2) is to be combined with the pressure meter A (FIGS. 1(a) and 1(b)), the pressure switch 32 and the pressure meter A have to be separately constructed. As a consequence, the cost of manufacture is high, and the accuracy cannot be increased substantially. The area taken up by the pressure meter A itself and the area occupied by the pressure switch 32 are so large that they will become a large obstacle to efforts to utilize the space in a factory where they are employed.
The unit of pressure generally used on pressure meter is kgf/cm.sup.2. Other units of pressure are PSI, KPa, MPa, and bar. The units used vary from country to country and from field to field. It has been customary to fabricate pressure meters of different kinds to meet customer's demands for the various units of pressure.
Therefore, different pressure meters have been manufactured for the reason of different units of pressure used, though substantially the same pressures are measured by the pressure meters. This results in the production of a small quantity of pressure meters in each of many different pressure meter types. Therefore, the efficiency and cost of production of pressure meters have been low and high, respectively.